low liquid level in sight glass?

[Jackson-B]

I work mainly on heating and air systems for residential and commercial applications, but I am attempting to convert a small 6000 btu R22 window unit into a glycol chiller for cooling a fermentation tank. when I start the system it runs great untill my glycol temp gets down to about 40 degrees and my suction pressure drops to around 45 psi. I noticed that my sight glass after the condenser is 1/2 full what is the reason for this, and what should I do. I do not usually work with temps. this low. I would appreciate any coments. Thanks.

[Gary]

We can't see it from here, so you will need to describe the system in more detail.

For starters, is it TXV or cap tube?

[lowcool]

fermentation at this temp would be like watching paint dry

[Jackson-B]

I am using a coil of 3/8 copper for my evaporator, that is in a cooler full of glycol. I have a circulating pump that pumps the cooled glycol through a coil around the fermenter.The evaporator coil is a total of 25 feet of tubing, and I am using the cap tube that was on the original evaporator for my metering device it is about 10 inches long. I am not shure what the size of the cap tube is. I tried a .031 at first but I could not get any suction pressure I tried several different lengths.

[Gary]

I could not get any suction pressure


That doesn't make any sense.

[Gary]

How did you charge the system?

[Magoo]

What is discharge pressure, if low, try blanking condenser off and getting discharge pressure up.
magoo

[Jackson-B]

with the small cap tube my suction pressure was -10 psi. with the larger cap tube with a glycol temp of 60 degrees my suction pressure starts at 70 psi and my liquid pressure is 225 psi. I charged the system at the starting water temp to a superheat of 20 degrees, and no bubble in my sight glass. When my glycol temp drops to 40 degrees my suction pressure falls to around 45 psi and my liquid pressure to 150 psi. Would it make a difference if I split my evaporator into two circuits. thank you.

[lowcool]

got to agree with magoo,i would be giving that a go first 215-230 psi and see if you achieve target temperature ??then tune your capillary if not.dont be to concerned about a clear sightglass being a capillary system,some bubbles are what you would expect,maybe someone can enlighten us both as to why(liquid bank up,flooding back?).experience with capillary systems in the past has always shown bubbles present.must say i am curious as to what your fermenting the driest cider in the world perhaps?

[Magoo]

Best advise is discard the RAC condensing unit and capilary, start again with a commercial condensing unit and fit a MOP thermostaic expansion valve. Both selected to match duty. The advantage of MOP TX' vav is that compressor does not overload during pull down. The TXV then controls liquid flow rate.
With capillary systems, the flow rate is dicatated by differential pressures. Add that high pressure / temp compressor really drop down in performance at low suction pressures and generally overheat, add over condensing equals low flow rates, the whole system goes flat and into a death spiral. Just like the situation you currently have.
Consider heat pumps, they always have cap tubes and condensing pressure control, ie flow rates.
magoo

[Gary]

I charged the system at the starting water temp to a superheat of 20 degrees, and no bubble in my sight glass. When my glycol temp drops to 40 degrees my suction pressure falls to around 45 psi...

As load drops, superheat drops... so the compressor should be pumping liquid at this point... or the suction valves gone.

[Jackson-B]

I am fermenting beer. Mostly ales but I would like to do lagers in the summer also. My fermentation temp is between 65-68 degrees for ales, and in the 30's for lager. It is done in my garage where summer time temps are in the 80's-90's The reason I am trying to use the small ac is because my wife does not like my hobby as much as I do and would flip out if I bought a chiller, and parts are easy for me to come by while i am experimenting with this.

[lowcool]

sounds like you gotta sort the wife out,me & a mate do ginger beer as well this maybe one way to swing her over.we dont brew at such temps,26 deg c for draughts etc,10-15 deg c for lagers.Coopers brewery in south australia have been exporting tins to the states for a while now & Brigalow make the ginger beer tins.cheers

[Gary]

Here's the easy way:

Get another cheap window shaker.

Get a Rubbermaid Slim Cooler.

Being careful not to break or kink the lines, place the window unit evaporator in the cooler.

Fill the cooler with your glycol solution.

Hook up your glycol pump.

Run the window unit.